(a) Field
The described technology relates generally to an acknowledgement (ACK) method and an uplink multi-user transmission method. More particularly, the described technology relates generally to an acknowledgement (ACK) method and an uplink multi-user transmission method in a wireless local area network (WLAN).
(b) Description of the Related Art
In a WLAN, data are transmitted and received by using unlicensed band such as 2.4 GHz or 5 GHz. The WLAN is being standardized by the IEEE (Institute of Electrical and Electronics Engineers) Part 11 under the name of “Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specifications.”
After an original standard was published on 1999, new version standards are continuously published by amendments. The IEEE standard 802.11a (IEEE Std 802.11a-1999) supporting 2.4 GHz band was published on 1999, and the IEEE standard 802.11g (IEEE Std 802.11g-2003) supporting 5 GHz band was published on 2003. These standards are called legacy. Subsequently, the IEEE standard 802.11n (IEEE Std 802.11n-2009) for enhancements for higher throughput (HT) was published on 2009, and the IEEE standard 802.11ac (IEEE 802.11ac-2013) for enhancements for very high throughput (VHT) was published on 2013. Recently, a high efficiency WLAN (HEW) for enhancing the system throughput in high density scenarios is being developed by the IEEE 802.11 ax task group.
A multiple input multiple output (MIMO) has been introduced by the HT WLAN, and a downlink multi-user MIMO (MU-MIMO) has been introduced by the VHT WLAN. Accordingly, a transmitting device with multiple antennas can simultaneously transmit downlink data to a plurality of receiving devices. However, an uplink MU-MIMO has not been introduced by the previous WLANs, but the HEW or a later WLAN may use the uplink MU-MIMO such that a plurality of transmitting devices can simultaneously transmit data to a single receiving device.
The HEW or later WLAN may use a scheme such as an orthogonal frequency division multiple access (OFDMA) for simultaneously transmitting data to a plurality of devices or for data being simultaneously transmitted by the plurality of devices.
A single physical layer convergence procedure (PLCP) protocol data unit (PPDU) including MAC protocol data units (MPDUs) having a plurality of access categories (ACs) can be transmitted in the VHT WLAN. In this case, an MPDU corresponding to one AC is transmitted to a single receiving device. However, the single device may receive MPDUs having the plurality of ACs in the HEW or later WLAN.
As such, since the single device may simultaneously receive data from the plurality of devices or may receive data with the plurality of ACs in the HEW or later WLAN, an ACK procedure for the received data is required.